Pressure actuated valve with improved slit configuration

ABSTRACT

A valve apparatus for medical applications, comprises a flexible member extending across a lumen through which a flow of materials is to be controlled. The flexible member includes a plurality of movable elements formed on opposite sides of a slit extending through the flexible member. The moveable members are biased so that when a pressure less than a predetermined threshold value is applied to the flexible member, the moveable elements are maintained in a closed position in which no flow is permitted past the flexible member and, when a pressure at least as great as the threshold value is applied to the flexible member, the moveable elements are moved to an open position separated from one another along the slit permitting flow through the lumen.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a continuation of, and claims priority to, copendingU.S. application Ser. No. 10/630,885, filed on Jul. 30, 2003.

BACKGROUND INFORMATION

Many medical procedures require repeated and prolonged access to apatient's vascular system. For example, during dialysis treatment bloodmay be removed from the body for external filtering and purification, tomake up for the inability of the patient's kidneys to carry out thatfunction. In this process, the patient's venous blood is extracted,processed in a dialysis machine and returned to the patient. Thedialysis machine purifies the blood by diffusing harmful compoundsthrough membranes, and may add to the blood therapeutic agents,nutrients etc., as required before returning it to the patient's body.Typically the blood is extracted from a source vein (e.g., the venacava) through a catheter sutured to the skin with a distal needle of thecatheter penetrating the source vein.

It is impractical and dangerous to insert and remove the catheter foreach dialysis session. Thus, the needle and catheter are generallyimplanted semi permanently with a distal portion of the assemblyremaining within the patient in contact with the vascular system while aproximal portion of the catheter remains external to the patient's body.The proximal end is sealed after each dialysis session has beencompleted to prevent blood loss and infections. However, even smallamounts of blood oozing into the proximal end of the catheter may bedangerous as thrombi can form therein due to coagulation which thrombimay then be introduced into the patient's vascular system when bloodflows from the dialysis machine through the catheter in a later session.

A common method of sealing the catheter after a dialysis session is toshut the catheter with a simple clamp. This method is oftenunsatisfactory because the repeated application of the clamp may weakenthe walls of the catheter due to the stress placed on the walls at asingle point. In addition, the pinched area of the catheter may not becompletely sealed allowing air to enter the catheter which may coagulateany blood present within the catheter. Alternatively, valves have beenused at the opening of the catheter in an attempt to prevent leakingthrough the catheter when the dialysis machine is disconnected. However,the unreliability of conventional valves has rendered themunsatisfactory for extended use.

SUMMARY OF THE INVENTION

In one aspect the present invention is directed to a valve apparatus formedical applications, comprising a flexible member extending across alumen through which a flow of materials is to be controlled. Theflexible member includes a plurality of movable elements formed onopposite sides of a slit extending through the flexible member. Themoveable members are biased so that when a pressure less than apredetermined threshold value is applied to the flexible member, themoveable elements are maintained in a closed position in which no flowis permitted past the flexible member and, when a pressure at least asgreat as the threshold value is applied to the flexible member, themoveable elements are moved to an open position separated from oneanother along the slit permitting flow through the lumen.

In a different aspect, the present invention is directed to a dialysisconnector comprising a valve housing having a first end connectable to apatient line and a second end mounted to a dialysis line and a flowpassage of the housing being connected to the patient line and beingoperatively connectable to the dialysis line in combination with a valveelement mounted within the flow passage of the housing, the valveelement including a flexible member extending across the flow passage,the flexible member including a plurality of movable elements formed onopposite sides of a first slit extending through the flexible member,the moveable members being biased so that, when a pressure less than apredetermined threshold value is applied to the flexible member, themoveable elements are maintained in a closed position in which no flowis permitted past the flexible member and, when a pressure at least asgreat as

the threshold value is applied to the flexible member, the moveableelements are moved to an open position separated from one another alongthe first slit permitting flow through the flow passage.

In yet another aspect, the invention is directed to a flow shutoffdevice for medical applications comprising a housing attachable to apatient line and a pressure actuated valve mounted within the housing toselectively restrict flow therethrough, wherein movable elements of thevalve are biased toward a closed position and are movable to an openposition when a pressure applied to the valve exceeds a predeterminedthreshold value. Flow through the housing is prevented when the movableelements are in the closed position.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a vascular access catheter;

FIG. 2 is a schematic drawing of a vascular access catheter inserted ina patient's vein;

FIG. 3 is a top elevation view of a valve element according to anexemplary embodiment of the present invention;

FIG. 4 is a top elevation view of a valve element according to anotherembodiment of the present invention;

FIG. 5 is a top elevation view of a valve element with double horizontalslits according to an embodiment of the present invention;

FIG. 6 is a top elevation view of a valve element with V-configuredslits according to an embodiment of the present invention; and

FIG. 7 is a top elevation view of a valve element with a curved slitaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Semi-permanently placed catheters may be useful for a variety of medicalprocedures which require repeated access to a patient's vascular systemin addition to the dialysis treatments mentioned above. For example,chemotherapy infusions may be repeated several times a week for extendedperiods of time. For safety reasons, as well as to improve the comfortof the patient, injections of these therapeutic agents may be bettercarried out with an implantable, semi-permanent vascular accesscatheter. Many other conditions that require chronic venous supply oftherapeutic agents, nutrients, blood products or other fluids to thepatient may also benefit from implantable access catheters, to avoidrepeated insertion of a needle into the patient's blood vessels. Thus,although the following description focuses on dialysis, those skilled inthe art will understand that the invention may be used in conjunctionwith any of a wide variety of procedures which require long termimplantation of catheters within the body.

Examples of such implantable catheters include those manufactured byVaxcel™, such as the Chronic Dialysis Catheter and the ImplantableVascular Access System. These devices typically are inserted under thepatient's skin, and have a distal end which includes a needle used toenter a blood vessel. The devices also have a proximal end extendingoutside the body for connection with an outside line. Thesesemi-permanent catheters may be sutured to the patient's skin tomaintain them in place while the patient goes about his or her normaloccupations.

FIGS. 1 and 2 show an exemplary implantable catheter for kidneydialysis. Catheter 10 has a distal end 12 that is insertable under theskin and into the patient's vein, and which remains within the patient'sbody for the life of the catheter 10. For example, catheter 10 mayremain implanted in the patient for two years. As shown more clearly inFIG. 2, distal end 12 fits within a vein 8 (e.g., the vena cava). Duringdialysis, blood from the patient is removed through a patient line suchas catheter 10, and is purified by a dialysis machine (not shown) whichis connected to hubs 18 and 20 of catheter 10 by a dialysis line.Catheter 10 in this example includes two lumens 22 and 24 which are usedrespectively to remove blood from and reintroduce blood to the vessel 8.Lumen 22 terminates at an inflow tip 14 formed at the distal end 12 ofthe catheter 10 while lumen 24 terminates at an outflow tip 16 formed atthe distal end 12. Inflow tip 14 and outflow tip 16 are connected tocorresponding inflow and outflow hubs 18, 20, which are accessibleoutside the body and which may be connected to external lines leading toand from the dialysis machine.

After the dialysis or other. procedure has been completed, the catheter10 is disconnected from the dialysis machine, and is left within thepatient fluidly coupled to the patient's vascular system. When notconnected to a dialysis machine, the catheter 10 is securely sealed toprevent fluids and gases from crossing into the proximal end of catheter10 by preventing flow in and out of catheter 10 through hubs 18, 20. Aswould be understood by those skilled in the art, this sealing preventsthe risks associated with infections and thrombi which might beexperienced if air or other gas or liquid and/or pathogens were to passinto the catheter 10.

As indicated above, although conventional clamps or clips may be used toseal the catheter 10 between medical sessions, over time the wall of thecatheter 10 may be damaged in the area to which the clamp or clip isapplied. Sealing clamps or clips may also become dislodged duringpatient activities, increasing the risk of leaks, infections, etc.Placing a clamp on the catheter 10 also increases the bulk of the distalend of the catheter which is exposed outside the patient's body, and mayadversely affect patient comfort.

Therefore, the catheter 10 includes one or more self sealing valvesalong each of the lumens 22, 24 to seal them when not being used duringdialysis and other transfusion or infusion sessions. For example, hubs18, 20 may be used to house one or more valves each of which is designedto seal the corresponding lumen 22, 24 under certain conditions, and toallow passage of fluids under other conditions. For example, in the caseof dialysis treatment, the system of valves may seal the catheter 10when it is not connected to an operating dialysis machine, and may allowboth an outflow of non-purified blood and an inflow of purified blood tothe patient when an operating dialysis machine is connected thereto.

Preferably, a valve system for use in such semi-permanent cathetersshould, when in the open position, allow a flow rate therethrough whichis sufficient to allow the procedure to be completed in an acceptablyshort time. When in the closed position, the valve should completelyseal the catheter. That is, if the valve requires excessive force to beopened, the flow rate through the catheter may be reduced to the pointwhere the time required for the procedure is unacceptably extended. Inaddition, a valve system having moving parts of too great a bulk mayalso result in larger blockages within the catheter or the hub housingthe valve thereby reducing the flow rate through the catheter. Themechanism that moves the valve into the open and closed positions mayblock the flow through the valve if it protrudes into the flow passage,and thus the size and bulk of the mechanism should preferably beminimized to avoid impeding flow through the open valve.

The portion of the valve that moves to the open position must alsocompletely return to the closed position when the session is completed.For example, a pressure sensitive valve may be used, which opens inresponse to a pressure driving the flow through the catheter. In thecase of a dialysis catheter, the valve or valves may open when apressure generated by the dialysis machine exceeds a predeterminedthreshold to allow circulation and purification of the patient's blood.When the dialysis machine is turned off and the pressure in the dialysisline is reduced below the threshold, the valve is completely sealed toprevent further flow from and to the patient. Some pressure is alsopresent in the patient line connecting the valve to the patient's veinas a result of the circulation in the patient's vascular system. Each ofthe valves must therefore be designed so that it will not respond tosuch pressure variations introduced by the vascular system and will notopen unless a pressure above the threshold is generated externally, forexample, by a dialysis machine.

The exemplary embodiments according to the present invention describedherein obtain both a secure closure of a semi-permanent catheterimplanted in a patient when the catheter is not in use and permit a flowpassage that is easily opened to allow a sufficient flow rate whenaccess to the vascular system is necessary.

In many applications, the pressure actuated valve system remains openfor the entire length of a therapeutic session, which may last asignificant amount of time. For example, in the case of a dialysissession, the valve system may remain open for up to four hours at atime, during sessions carried out up to three times a week. Theexemplary embodiments of valves according to the present inventionprovide a seal to the catheter even after being maintained in the openposition for prolonged periods of time.

Specific embodiments of the present invention will be described belowwith reference to the drawings. FIG. 3 shows a top plan view of anexemplary embodiment of a valve element 100 used to control the flowthrough a medical tube such as the catheter 10 of FIG. 1. For example,valve element 100 may be located in a flow passage within a valvehousing formed in either or both of the hubs 18, 20, through whichfluids flow to and from the distal end 12. As will be apparent to thoseskilled in the art, the valve housing may be placed at any otherlocation along the length of catheter 10 and may be unitary with thecatheter 10, or may be formed as a separate component. In addition, itwill be apparent that a single valve housing with dual flow passages andone valve 100 within each of the flow passages may be provided insteadof two separate valve housings for the hubs 18, 20, respectively, toindependently control fluid flow in each direction. Inflow to thepatient may take place via one of the dual flow passages of the singlehub, and outflow from the patient via the other flow passage.

In the exemplary embodiment shown in FIG. 3, the valve element 100 isformed as a flexible disk 110 having dimensions appropriate to the sizeof the flow passage within the one of the hubs 18, 20 into which it isto be mounted. The flexible disk 110 may be formed of any sufficientlyflexible material, such as a polymeric material. More specifically, theflexible disk 110 may be formed of silicone. The flexible disk 110 mayalso include a peripheral portion 116 adapted to be connected to aninner surface of the flow passage to seal perimeter of the flow passagearound flexible disk 110. The valve element 100 includes a slit 112which extends through the entire thickness of the flexible disk 110. Theslit 112 separates two movable elements 118 from one another to form anopenable portion of the disk 110 which creates a flow passagetherethrough when the movable elements 118 are placed in an openposition separated from one another. For example, when the edges 120 ofthe movable elements 118 are moved out of the plane of the flexible disk110, an opening through the flexible disk 110 is formed along the slit112. In this exemplary embodiment, the movable elements 118 are formedas resilient flaps substantially constrained in all directions exceptalong the slit 112. Accordingly, the elements 118 are substantiallyconstricted and may only move along the edges 120 to form a relativelysmall opening.

In one exemplary embodiment the valve element 100 is used in conjunctionwith dialysis equipment, and movement of movable elements 118 to theopen position is prompted by an actuating pressure of a fluid withindialysis lines 30, 32 which may be connected to the hubs 18, 20,respectively, to connect the catheter 10 to a dialysis machine. Inparticular, an actuating pressure is generated by pumps in the dialysismachine to move the patient's blood between the patient and thefiltration equipment. Although the movable elements 118 are formed asflexible flaps, they are formed with a predetermined amount ofresilience to allow them to remain in the closed position when not actedupon by the pressure in dialysis lines 30, 32. Specifically, theelements 118 are biased to remain in the closed position abutting oneanother along edges 120 at all times when they are not acted on by apressure outside a range of approximately 22 to 44 mmHg. Specifically,as mentioned above, the elements 118 are formed so that the amount ofresilience is sufficient to maintain them in the closed position withoutbeing forced open by fluid forces generated by natural circulation ofthe patient's blood. As would be understood by those skilled in the art,the amount of pressure required to open the movable elements 118 is afunction of the resilience of the material forming those elements, thesize and shape of the slit 112, and the size of the flow passagecontaining the valve element 100. The details of the geometry of theslit 112 and the movable elements 118 may be selected to obtain thedesired characteristics of maximum flow in the open position, and toensure that valve element 100 seals the flow passage when the pressureis removed.

A stiffening element 114 may be included in valve element 100, to bettercontrol the amount of force biasing the movable elements 118 to theclosed position. In particular, coupling a stiffening element to anotherwise flexible disk 110 (or forming a stiffening element integrallytherewith) provides a valve element 100 including movable elements 118more resistant to plastic deformation during sessions lasting multiplehours in which the valve element 100 is kept open. An example of asuitable stiffening member is the addition of stiffening ring 114 to theflexible disk 110. The stiffening element 114 may, for example, beformed of a wire or embedded within the valve element 100. Of course,those skilled in the art will understand that the stiffening element 114may be formed of metal, plastic or any substantially rigid material.

In one exemplary embodiment, the stiffening ring 114 may be embeddedwithin the material of the disk 110, to minimize the bulk of thecombination. In different embodiments, stiffening elements may be bondedto one or both sides of the valve element 100, depending on therequirements of the use of the valve element 100. The shape of thestiffening elements used in the valve element 100 may also be modified,depending on the desired characteristics of the force urging the movableelements 118 to the closed position. Alternatively, the stiffeningelements may be integrally formed with the disk 110.

As indicated above, the maximum flow that can pass through valve element100 and the ability to close fully when the actuating pressure isremoved are important design parameters for the pressure actuated valvesdescribed herein. According to embodiments of the invention, thesedesign parameters may be controlled by properly shaping and sizing theslit or slits 112. Selection of the dimensions of the slit 112 resultsin movable elements 118 having a desired shape and being constrainedalong selected edges. In the exemplary embodiment shown in FIG. 3, alinear slit having a width d of approximately 0.002 inches and a lengthof approximately 0.150 to 0.280 inches is provided in the center of anoval flexible disk 110 extending along a major axis of the disk. Theflexible disk 110 could have a thickness of approximately 0.015 to 0.030inches and could be manufactured from silicone, as a result its surfaceresistivity rating would be approximately 35 to 70 A. The movableelements 118 used in this configuration are flaps that form an openingby deflecting away from the plane of the disk 110 due to theirflexibility, since they are constrained along all sides except along theslit 112. This configuration provides satisfactory performance in adialysis catheter application, with the catheter having conventionaldimensions and providing conventional flow rates. For example, thepressure to which the valve may be subjected during dialysis may be inthe range of 200 to 285 mmHg while the pressures applied to the valve bythe patient's vascular system are expected to remain below 22 mmHg.Thus, the valve system will preferably be designed to remain sealed whennot subjected to a pressure of at least 44 mmHg and, when subjected tothe a pressure above that threshold should preferably allow a flow rateof at least 300 ml/min and more preferably at least 350 ml/min withoutsubstantially failing to meet these criteria during a life span of oneor more years while being subjected to 3 or more uses of up to 4 hourseach per week.

The performance characteristics of the valve element 100 can be furthertuned by selecting an appropriate length/of the slit 112. By alteringthis length l, both the maximum flow rate and the opening/closingperformance of the valve element 100 will be changed. For example,increasing the length of the slit 112, other parameters being the same,increases a maximum size of the opening through the flexible disk 110,and makes it easier to displace the movable elements 118 to the openposition as they are unconstrained along longer edges 120. For the samereason, the movable elements 118 are subjected to a reduced forcebiasing them toward the closed position when the actuating pressure isremoved. Both the width d and the length/of the slit 112 are selected asa tradeoff between ease/size of the opening and the biasing forceclosing the valve element 100 after use.

A different exemplary configuration of slits to define the movableelements is shown in FIG. 4. In this embodiment, a flexible disk 210 isprovided with slits 212, 214 in a substantially H-shaped configurationthat define movable elements 218. The slit 212 is a substantially linearslit aligned with a major dimension of the disk 210, and the slits 214extend substantially perpendicular to slit 212, disposed nearterminating points thereof. This configuration of slits permits themovable elements 218 to more easily move to the open configuration,since each movable element 218 is unconstrained along both the slit 212and the slits 214. The pressure generated by an external pump, such as adialysis pump, thus can more easily force the movable elements 218 tothe open position. The two additional unconstrained sides of the movableelements 218 also form a larger open area of the flexible disk 210, sothat a greater flow rate can pass through the valve element 200.

Additional resilient elements may also be used in the exemplaryembodiment shown in FIG. 4 to achieve desired closing characteristics ofthe valve element 200. For example, a pair of resilient elements 220 maybe disposed substantially parallel to the slit 212 on either sidethereof. The resilient elements 220 control the deflection and provide aforce biasing the movable elements 218 toward the closed position alongthe axis of the slit 212. Those skilled in the art will understand thatadditional resilient elements 222 may be used to increase the biasingforce and/or to control the deflection of the movable elements 218 alongan axis parallel to the slits 214. This exemplary combination ofH-configured slits and corresponding H-configured resilient elementsresults in a high flow, easily opened pressure actuated valve element200, which is able to completely return to the closed position once theactuating pressure is removed. This configuration also resists plasticdeformation that may occur when valve elements are kept in the openposition for extended periods of time, and which may prevent the valvefrom fully closing due to retaining a “memory” of the open position.

Another exemplary embodiment according to the present invention isdepicted in FIG. 5. In this embodiment, a double horizontal slit is usedto define the movable elements of a valve element 250. Morespecifically, a pair of substantially parallel slits 262 extends throughthe flexible disk 260, substantially along a major dimension thereof. Inthe case of a substantially elliptical flexible disk 260, as shown, theslits 262 are substantially parallel to a major axis of the ellipse. Amovable element 264 is thus defined substantially at the center of theflexible disk 260, and is constrained only at ends 265 thereof neartermination points of the slits 262.

The greater unconstrained length of the sides of the movable element 264along the slits 262, enables a large flow area to open as a result of anactuating pressure. For the same reason, a relatively low actuatingpressure is needed to open the movable element 264. To ensure a completeclosing of valve element 250 when the actuating pressure is removed, forexample, resilient elements may be added around the slits 262 to furtherbias the movable element 264 to the closed position. In the exemplaryembodiment shown in FIG. 5, resilient elements 266, 268 are disposed ina substantially rectangular configuration surrounding the slits 262. Inthis configuration the resilient elements 266, 268 control thedeflection of the movable element 264 in directions substantiallyparallel and perpendicular to the slit orientation and provide a biasingforce that closes the movable element 264 when the actuating pressure isremoved. The resilient elements 266, 268 may form a complete rectangle,or may be separated at the vertices.

FIG. 6 shows yet another embodiment of the pressure actuated valveaccording to the present invention. In this exemplary embodiment, alinear slit is combined with a pair of V-configured slits to provide alarger flow area when the valve element is placed in the open positionby an actuating pressure thereagainst. As shown in the drawing, thevalve element 300 is formed as a flexible disk 310 which, in thisexample, has a substantially elliptical shape. It will be apparent tothose skilled in the art that different shapes of the flexible disk 310may be used, depending on the shape and dimensions of the housing inwhich the valve element 300 is placed. A linear slit 312 is formed inthe flexible disk 310, for example along a major dimension thereof, andis complemented by two pairs of slits 314. A first pair of the slits 314is disposed at a first end of the slit 312 with a second one of thepairs of slits 314 being formed at the second end of the slit 312. Theslits 314 are formed at an angle with the slit 312, so that, at each endof the slit 312, a substantially V-shaped configuration of slits isformed.

In the exemplary embodiment shown, the slits 312 and 314 do not touchone another so that the movable elements 320 are continuous withportions 322 of the flexible disk 320. In different embodiments, theslits 312 and 314 may intersect with one another, breaking the flexibledisk 320 into additional distinct moving elements. In the exemplaryembodiment shown, the movable elements 320 are unconstrained along theslits 312, 314, but are constrained in the region between the slits bybeing continuous with the portions 322 of the flexible disk 320. Theaddition of the Y configured slits permits the movable elements 320 toopen to a greater extent under an actuating pressure, while retaining abiasing force sufficient to close the opening when the actuatingpressure is removed. To further bias the movable elements 320 toward theclosed position, resilient elements 316,318 may be added. As discussedin the context of previous embodiments, the resilient elements 316,318may be disposed in a substantially rectangular pattern around the slits312,314 to control the deflection and closure of the movable elements320 in two perpendicular directions. The resilient elements 316, 318 mayform a completely rectangular enclosure as shown in FIG. 6, or may haveopen vertices, as shown in previous embodiments. As would be understoodby those skilled in the art, the relative size and orientation of theslits 312, 314 may be selected to give desired flow and closingproperties, for a given flexible disk 320.

A further exemplary embodiment of the invention is depicted in FIG. 7.In this example, the valve element 350 comprises a flexible disk 360having a slit 362 extending therethrough. The slit 362 is not a linearslit, but instead is curved about a principal axis of the flexible disk360. In the example shown in FIG. 7, the slit 362 follows a generallysinusoidal path. However other curved paths may be used with similareffect. The slit 362 defines two movable elements 364, 366 which arecomplementary to each other on opposite sides of the slit 362. A benefitof this configuration is that, for a given length/of the slit 362, alarger opening area of the valve element 350 may be obtained. Since theunconstrained edges of the movable elements 364, 366 are longer due totheir curved shape, a given actuating pressure is able to displace alarger portion of the movable elements 364, 366 to the open position.This allows for a larger flow area through the valve element 350.

As was the case in other exemplary embodiments of the invention, theresilience of the movable elements 364, 366 is controlled to ensure thevalve fully closes once the actuating pressure is removed, and is notsubject to “memory” effects after being open for extended periods oftime. Accordingly, the resilience of the material forming the movableelements 364, 366 can be controlled, and additional resilient elementsmay be incorporated in the flexible disk 360, as described above withrespect to other embodiments.

The present invention has been described with reference to specificexemplary embodiments. Those skilled in the art will understand thatchanges may be made in details, particularly in matters of shape, size,material and arrangement of parts. For example, different flexible disksmay be used to form the pressure sensitive valve, and may have differentdimensions than those shown. Furthermore, as would be understood bythose of skill in the art, any of the various features of the differentembodiments described may be combined in any manner to take advantage oftheir various properties. Accordingly, various modifications and changesmay be made to the embodiments without departing from the broadest scopeof the invention as set forth in the claims that follow. Thespecifications and drawings are, therefore, to be regarded in anillustrative rather than a restrictive sense.

1-27. (canceled)
 28. A valve for use in medical applications,comprising: a flexible disk having a plurality of moveable elements, themoveable elements having open and closed configurations; and at leastone stiffening element disposed adjacent to the moveable elements,wherein the stiffening element is configured to hold the moveableelements in the closed configuration when acted upon by fluid pressuresless than a predetermined threshold.
 29. The valve according to claim28, wherein the stiffening element is ring shaped and encircles themoveable elements.
 30. The valve according to claim 28, wherein thestiffening element is substantially rectangular and surrounds themoveable elements.
 31. The valve according to claim 28, wherein thestiffening element is wholly embedded within the flexible disk.
 32. Thevalve according to claim 28, wherein the stiffening element is bonded toa surface of the flexible disk.
 33. The valve according to claim 28,wherein the stiffening element is integrally formed with the flexibledisk.
 34. The valve according to claim 28, wherein the predeterminedthreshold is between approximately 22 mmHg and 44 mmHg.
 35. The valveaccording to claim 28, wherein the moveable elements are formed as edgesof a slit through the flexible disk, and wherein the edges are adjacentto one-another in the closed configuration but are separated fromone-another in the open configuration.
 36. The valve according to claim35, wherein the disk includes a plurality of slits that are non-paralleland non-intersecting.
 37. The valve according to claim 35, wherein thedisk includes a plurality of slits that are non-parallel and thatintersect.
 38. The valve according to claim 35, wherein the diskincludes a plurality of slits that are parallel.
 39. The valve accordingto claim 35, wherein the disk includes at least one curved slit.
 40. Thevalve according to claim 35, wherein the disk includes a slit that isS-shaped.
 41. A valve for use in medical applications, comprising: aflexible disk having a plurality of moveable elements, the moveableelements having open and closed configurations; and a plurality ofstiffening elements disposed around the moveable elements, wherein thestiffening elements are configured to hold the moveable elements in theclosed configuration when acted upon by fluid pressures less than apredetermined threshold.
 42. The valve according to claim 41, whereinthe stiffening elements are parallel and are disposed alongside themoveable elements.
 43. The valve according to claim 41, wherein thestiffening elements are disposed in a substantially rectangulararrangement about the moveable elements.
 44. The valve according toclaim 41, wherein the stiffening elements are wholly embedded within theflexible disk.
 45. The valve according to claim 41, wherein thestiffening elements are bonded to a surface of the flexible disk. 46.The valve according to claim 41, wherein the stiffening elements areintegrally formed with the flexible disk.
 47. The valve according toclaim 41, wherein the predetermined threshold is between approximately22 mmHg and 44 mmHg.
 48. The valve according to claim 41, wherein themoveable elements are formed as edges of a slit through the flexibledisk, and wherein the edges are adjacent to one-another in the closedconfiguration but are separated from one-another in the openconfiguration.
 49. The valve according to claim 48, wherein the diskincludes a plurality of slits that are non-parallel andnon-intersecting.
 50. The valve according to claim 48, wherein the diskincludes a plurality of slits that are non-parallel and that intersect.51. The valve according to claim 48, wherein the disk includes aplurality of slits that are parallel.
 52. The valve according to claim48, wherein the disk includes at least one curved slit.
 53. The valveaccording to claim 48, wherein the disk includes a slit that isS-shaped.